1. Field of the Invention
The subject invention is generally related to endless conveyors and is specifically directed to a conveyor system having zero back-pressure when advancement of conveyed articles is interrupted downstream.
2. Description of the Prior Art
Endless conveyor systems are well known. An example of a zero back-pressure conveyor is shown and described in U.S. Pat. No. 5,085,311; entitled: IN-LINE ACCUMULATOR WITH ZERO BACKLINE PRESSURE; issued to G. Garro on Feb. 4, 1992. As there shown, an endless chain or belt conveyor includes a pair of wear surfaces, one on either side of the belt to support the products being advanced by the chain. The belt is adapted to be displaced downwardly away from the chain when advancement downstream is interrupted, thereby permitting the conveyed articles to be supported only by the wear surfaces. A similar device is shown in Japanese Patent Document No. 0145018, dated Jul. 2, 1986.
While the claims of the Garro patent are limited to displacement of the belt or chain, with the wear surfaces stationary, the Garro patent also discloses an alternative embodiment in FIGS. 4 and 5, wherein the horizontal position of the chain is fixed and the wear surfaces are displaced therefrom to lift the articles above the chain.
While a conceptually sound idea, since this eliminated displacement of the moving chain, the Garro design is impractical in practice. As shown in Garro, the segmented wear surfaces were designed to lift horizontally away from the belt, leaving displaced, exposed ends and creating a discontinuous wear surface or guide surface. While all of the articles fully positioned on the wear surface would be properly lifted from the chain when a section of the wear surfaces were displaced, those overhanging the end of the displaced section would be tipped, or could be caught up between wear surface sections. In addition, the upstream articles would continue to move on the chain and would butt against the raised wear surface section, being potentially exposed to damage when the wear surface section was lowered into position.
Due to the drawbacks of this design, zero back pressure systems have relied generally on the displacement of the chain in order to maintain a continuous guide or wear surface for the conveyed articles. However, it is desirable to provide a zero backline pressure system wherein the moving chain or belt does not need to be displaced.